Selected area electron diffraction data collection with Gatan counted cameras

Selected area electron diffraction (SAED) is a simple but powerful technique for determining the structure of materials in the electron microscope. Here we will describe the steps required to collect high-quality SAED data using the K3® or Metro® cameras. 

Camera setup for SAED data collection

  1. Reduce the beam’s intensity by changing the spot size to one of the highest numbers (smallest spot) available. 
  2. Insert a selected area aperture.
  3. With the microscope in transmission electron microscopy (TEM) mode, start the camera live view and change the magnification so the SA aperture is entirely within the field of view.
  4. Ensure the desired sample region is located within the selected area aperture.
  5. Decrease the beam intensity until fewer than 250,000 e-/s (K3) or 500,000 e-/s (Metro) reach the camera. The total electron dose rate can be measured easily if the entire SA aperture is being viewed within the field of view of the camera. Just multiply the dose rate (in e/pix/s) from the dose rate monitor at the bottom of the screen by the number of pixels in the live view image to get the total number of electrons per second.
  6. Switch the microscope to Diffraction mode and center the undeflected diffraction beam on the camera. 
  7. Using the Focus knob, adjust the central bright spot to a minimum diameter while viewing the pattern on the camera. These conditions should result in saturated pixels displaying a contrast reversal of the central diffraction beam. This contrast reversal is normal. 
  8. Set the camera length such that the desired range of reciprocal space is visible on the camera. For Metro, this camera length may be quite short. 

Note: If quantification of diffraction peak intensity is desired, keeping the brightest Bragg intensities below 40 e-/pix/s (K3) or 80 e-/pix/s (Metro) is essential. 

  1. Click Capture. Longer exposure times (10 – 100 s) will yield better signal-to-noise in high-resolution peaks.